1. Field of the Invention
The present invention relates to a semiconductor device which includes, as a circuit, a thin film transistor (hereinafter referred to as TFT) using a semiconductor thin film, and a technique regarding a method of manufacturing the same. Incidentally, in the present specification, the semiconductor device means any device which is made to function by using a semiconductor.
Thus, the term xe2x80x9csemiconductor devicexe2x80x9d recited throughout this specification includes not only a single semiconductor component such as a TFT, but also an electro-optical device with TFTS, a semiconductor circuit, and an electronic equipment having those.
2. Description of the Related Art
In recent years, a TFT used for an electro-optical device such as an active matrix type liquid crystal display device has been actively developed. The active matrix type liquid crystal display device is a monolithic display device in which a pixel matrix circuit and a driver circuit are provided on the same substrate.
Moreover, recently, an experiment of forming a semiconductor circuit having a function comparable to a conventional IC by using TFTs provided on a substrate has also been made. For example, the development of a system-on-panel having a built-in logic circuit such as a xcex3-correction circuit, a memory circuit, and a clock generating circuit has been under review.
Since such a driver circuit or a logic circuit is required to perform a high speed operation, it is unsuitable to use an amorphous semiconductor film (typically, an amorphous silicon film) as an active layer. Thus, under the present circumstances, a crystalline semiconductor film (typically, a polysilicon film) has been examined.
However, when circuit performance comparable to a conventional IC comes to be required for a circuit assembled with TFTS, such circumstances have occurred that it is difficult to manufacture a TFT having satisfactory performance to meet the circuit specification by using a crystalline semiconductor film formed through a conventional technique.
An object of the present invention is therefore to realize a high performance semiconductor device by manufacturing TFTs each having electrical characteristics superior to a TFT using a conventional polysilicon film and by assembling a circuit with the TFTs.
According to one aspect of the present invention disclosed in this specification, a method of manufacturing a semiconductor device is characterized by comprising:
a first step of forming a crystal-containing semiconductor film;
a second step of oxidizing the crystal-containing semiconductor film to decrease its thickness;
a third step of carrying out a laser annealing treatment with an energy density of 250 to 5000 mJ/cm2 to the crystal-containing semiconductor film after the second step; and
a fourth step of carrying out a furnace annealing treatment to the crystal-containing semiconductor film after the third step.
According to another aspect of the present invention, a method of manufacturing a semiconductor device is characterized by comprising:
a first step of forming a crystal-containing semiconductor film;
a second step of oxidizing the crystal-containing semiconductor film to decrease its thickness;
a third step of carrying out a laser annealing treatment with an energy density of 250 to 5000 mJ/cm2 to the crystal-containing semiconductor film after the second step; and
a fourth step of carrying out a furnace annealing treatment at 900 to 1200xc2x0 C. in a reduced atmosphere to the crystal-containing semiconductor film after the third step.
In the first step, the crystal-containing semiconductor film includes any semiconductor films containing crystalline components, and specifically indicates a single crystal semiconductor film, a polycrystal semiconductor film, a microcrystal semiconductor film, a semiconductor film of an amorphous semiconductor film only a part of which is crystallized, and a semiconductor film substantially regarded as a single crystal film.
Incidentally, the semiconductor film substantially regarded as the single crystal film indicates such a semiconductor film that although it is a semiconductor film formed of an aggregation of a plurality of crystal grains, it has such crystallinity that plane orientations of the respective crystal grains are uniform, that is, specific orientation is shown on the whole film surface.
Besides, the noncrystal-containing semiconductor film includes any semiconductor films containing amorphous components, and indicates a microcrystal semiconductor film, an amorphous semiconductor film, and a semiconductor film of an amorphous semiconductor film only a part of which is crystallized.
Besides, in the present specification, although a silicon film is cited as a typical example of the semiconductor film, it is needless to say that a semiconductor film such as a germanium film or a silicon germanium film (expressed by Si1xe2x88x92xGex (0 less than X less than 1)) can also be used in the present invention.
Besides, in the third step of carrying out the laser annealing treatment, it is appropriate that excimer laser light using an excitation gas such as KrF (wavelength 248 nm), XeCl (wavelength 308 nm), or ArF (wavelength 193 nm) is used. The beam shape of the laser light may be a linear shape or a planar shape.
Besides, light energy which can be used in the present invention is not limited to the excimer laser light, but ultraviolet light or infrared light may be used. In that case, intense light with light intensity comparable to laser light has only to be radiated from an ultraviolet lamp or an infrared lamp.
In the fourth step, although a treatment atmosphere in the furnace annealing treatment is not particularly limited, it is preferable to use a reduced atmosphere. The reduced atmosphere indicates a hydrogen atmosphere, an ammonia atmosphere, or an inert gas atmosphere containing hydrogen or ammonia (mixed atmosphere of hydrogen and nitrogen, mixed atmosphere of hydrogen and argon, and the like). Besides, it is preferable that a treatment temperature is made 900 to 1200xc2x0 C. (preferably 1000 to 1100xc2x0 C.).
This step first has an effect to flatten the surface of the crystal-containing semiconductor film. This is a result of enhanced surface diffusion of semiconductor atoms functioning to make the surface energy minimum. Besides, at the same time, this step has also an effect to greatly decrease defects existing in crystal grains and crystal grain boundaries. This effect is obtained through a terminating effect to uncombined bonds by hydrogen, a removing effect to impurities by hydrogen, and recombination of semiconductor atoms with the effect. For the purpose of obtaining these effects, the heat treatment at 900 to 1200xc2x0 C. in the reduced atmosphere is necessary.
Incidentally, flattening of the surface of the crystal-containing semiconductor film can be made in even an inert gas atmosphere (nitrogen atmosphere, helium atmosphere, or argon atmosphere). However, if reduction of a natural oxidation film is carried out by using a reducing function, a number of silicon atoms with high energy are produced and the flattening effect is consequently raised, so that the reduced atmosphere is preferable.
According to another aspect of the present invention, a method of manufacturing a semiconductor device is characterized by comprising:
a first step of forming a crystal-containing semiconductor film;
a second step of carrying out a laser annealing treatment with an energy density of 250 to 5000 mJ/cm2 to the crystal-containing semiconductor film;
a third step of carrying out a furnace annealing treatment to the crystal-containing semiconductor film after the second step; and
a fourth step of oxidizing the crystal-containing semiconductor film after the third step to decrease its thickness.
In the third step, although a treatment atmosphere in the furnace annealing treatment is not particularly limited, it is preferable to use a reduced atmosphere. The reduced atmosphere indicates a hydrogen atmosphere, an ammonia atmosphere, or an inert gas atmosphere containing hydrogen or ammonia (mixed atmosphere of hydrogen and nitrogen, mixed atmosphere of hydrogen and argon, and the like). Besides, it is preferable that a treatment temperature is made 900 to 1200xc2x0 C. (preferably 1000 to 1100xc2x0 C.).
This third step has an effect to further flatten the surface of the crystal-containing semiconductor film. This is a result of enhanced surface diffusion of semiconductor atoms functioning to make the surface energy minimum. Besides, at the same time, this step has also an effect to greatly decrease defects existing in crystal grains and crystal grain boundaries. This effect is obtained through a terminating effect to uncombined bonds by hydrogen, a removing effect to impurities by hydrogen, and recombination of semiconductor atoms with the effect. For the purpose of obtaining these effects, the heat treatment at 900 to 1200xc2x0 C. in the reduced atmosphere is necessary.
In the fourth step, the step of oxidizing the film to decrease its thickness may be carried out through a plurality of thermal oxidation steps. As means for oxidizing the film to decrease its thickness, it is possible to use thermal oxidation, plasma oxidation, or the like. Particularly, in the present invention, oxidation through the thermal oxidation is preferable. Incidentally, in the case of the plasma oxidation, if He is added in an oxygen atmosphere, an oxygen radical is easily produced. Thus, the addition of He is preferable. Besides, in the fourth step, it is possible to obtain an effect to flatten the roughness of the surface of the semiconductor film.
According to another aspect of the present invention, a method of manufacturing a semiconductor device is characterized by comprising:
a first step of forming a crystal-containing semiconductor film;
a second step of carrying out a laser annealing treatment with an energy density of 250 to 5000 mJ/cm2 to the crystal-containing semiconductor film;
a third step of carrying out a furnace annealing treatment at 900 to 1200xc2x0 C. in a reduced atmosphere to the crystal-containing semiconductor film after the second step; and
a fourth step of oxidizing the crystal-containing semiconductor film after the third step to decrease its thickness.
Further, according to another aspect of the present invention, a method of manufacturing a semiconductor device is characterized by comprising:
a first step of forming a crystal-containing semiconductor film;
a second step of carrying out a laser annealing treatment with an energy density of 250 to 5000 mJ/cm2 to the crystal-containing semiconductor film;
a third step of oxidizing the crystal-containing semiconductor film after the second step to decrease its thickness; and
a fourth step of carrying out a furnace annealing treatment to the crystal-containing semiconductor film after the third step.
Furthermore, according to another aspect of the present invention, a method of manufacturing a semiconductor device is characterized by comprising:
a first step of forming a crystal-containing semiconductor film;
a second step of carrying out a laser annealing treatment with an energy density of 250 to 5000 mJ/cm2 to the crystal-containing semiconductor film;
a third step of oxidizing the crystal-containing semiconductor film after the second step to decrease its thickness; and
a fourth step of carrying out a furnace annealing treatment at 900 to 1200xc2x0 C. in a reduced atmosphere to the crystal-containing semiconductor film after the third step.
In the third step, the step of oxidizing the film to decrease its thickness may be carried out through a plurality of thermal oxidation steps. As means for oxidizing the film to decrease its thickness, it is possible to use thermal oxidation, plasma oxidation, or the like. Particularly, in the present invention, oxidation through the thermal oxidation is preferable. In the case of the plasma oxidation, if He is added in an oxygen atmosphere, an oxygen radical is easily produced. Thus, the addition of He is preferable. Besides, in the third step, it is possible to obtain an effect to flatten the roughness of the surface of the semiconductor film.
In the fourth step, although a treatment atmosphere in the furnace annealing treatment is not particularly limited, it is preferable to use a reduced atmosphere. The reduced atmosphere indicates a hydrogen atmosphere, an ammonia atmosphere, or an inert gas atmosphere containing hydrogen or ammonia (mixed atmosphere of hydrogen and nitrogen, mixed atmosphere of hydrogen and argon, and the like). Besides, it is preferable that the treatment temperature is made 900 to 1200xc2x0 C. (preferably 1000 to 1100xc2x0 C).
This fourth step has an effect to further flatten the surface of the crystal-containing semiconductor film. This is a result of enhanced surface diffusion of semiconductor atoms functioning to make the surface energy minimum. Besides, at the same time, this step has also an effect to greatly decrease defects existing in crystal grains and crystal grain boundaries. This effect is obtained through a terminating effect to uncombined bonds by hydrogen, a removing effect to impurities by hydrogen, and recombination of semiconductor atoms with the effect. For the purpose of obtaining these effects, the heat treatment at 900 to 1200xc2x0 C. in the reduced atmosphere is necessary.
Incidentally, flattening of the surface of the crystal-containing semiconductor film can be made in even an inert gas atmosphere (nitrogen atmosphere, helium atmosphere, or argon atmosphere). However, if reduction of a natural oxidation film is carried out by using a reducing function, a number of silicon atoms with high energy are produced and the flattening effect is consequently raised, so that the reduced atmosphere is preferable.
Besides, in the first step of the above-described respective aspects, the crystal-containing semiconductor film includes any semiconductor films containing crystalline components, and specifically indicates a single crystal semiconductor film, a polycrystal semiconductor film, a microcrystal semiconductor film, a semiconductor film of an amorphous semiconductor film only a part of which is crystallized, and a semiconductor film substantially regarded as a single crystal film.
Incidentally, the semiconductor film substantially regarded as the single crystal film indicates such a semiconductor film that although it is a semiconductor film formed of an aggregation of a plurality of crystal grains, it has such crystallinity that plane orientations of the respective crystal grains are uniform, that is, specific orientation is shown on the whole film surface.
Besides, the noncrystal-containing semiconductor film includes any semiconductor films containing amorphous components, and indicates a microcrystal semiconductor film, an amorphous semiconductor film, and a semiconductor film of an amorphous semiconductor film only a part of which is crystallized.
Besides, in the present specification, although a silicon film is cited as a typical example of the semiconductor film, it is needless to say that a semiconductor film such as a germanium film or a silicon germanium film (expressed by Si1xe2x88x92xGex (0 less than X less than 1)) can also be used in the present invention.
Besides, in the second step of the above-described respective aspects, it is appropriate that excimer laser light using an excitation gas such as KrF (wavelength 248 nm), XeCl (wavelength 308 nm), or ArF (wavelength 193 nm) is used in the step of carrying out the laser annealing treatment. The beam shape of the laser light may be a linear shape or a planar shape.
Besides, light energy which can be used in the present invention is not limited to the excimer laser light, but ultraviolet light or infrared light may be used. In that case, intense light with light intensity comparable to laser light has only to be radiated from an ultraviolet lamp or an infrared lamp.